Diesel-electric locomotives traditionally employ a high power diesel internal combustion engine to rotate an electric generator, which in turn provides electric power to drive the locomotive's traction motors and to power other components. In a line haul locomotive, the need for accelerating and pulling many hundreds of tons of rolling stock and cargo up to high speeds with the traction motors requires a large amount of power. The diesel engine in a line haul locomotive often has a rated power output exceeding 4,000 brake horsepower (bhp).
Large diesel engines perform well in terms of emissions and fuel efficiency at or near the rated power output. But the duty cycle typically experienced by a line haul locomotive also requires the engine to idle for long periods of time or maintain low train speeds, which results in the diesel engine running at a power output much lower than its rated output, in addition to running at high power output when accelerating a large train of cargo. The large diesel engine is relatively less effective in terms of emissions and fuel efficiency at low power outputs. Considering this range of required power outputs—from running at or near the rated power while accelerating a train, to running at low power during idle—the large diesel engine is a compromise, delivering its best performance at high power outputs.
Recently several locomotive manufacturers in the U.S. have begun to commercialize new locomotives which are powered by multiple diesel engines. For instance, multi-engine “gen set” switcher locomotives developed by several competing manufacturers are being tested by railroads. These locomotives are called “gen set” locomotives because each engine and respective electric generator are mounted together on a separate frame as an independent power pack—similar to a generator set used in backup power or remote power applications—which is then individually mounted to the locomotive deck. The multi-engine “gen set” locomotives have been built with 2-4 separate, identical power packs. Having multiple engines allows the operation of just a single engine during idling and low power output. The relatively small, single engine operated during low power output can operate more efficiently than a very large diesel engine at that same power output. A low power output will be a much higher percentage of the rated power of a small engine than it would be for a very large engine, and efficiency is generally a function of the percentage of rated power output. When the locomotive requires high power output, all of the engines can be operated simultaneously to produce maximum power. Thus, with the application of multiple engines, it is possible to reach a new compromise for locomotive propulsion where power can be provided almost as effectively, in terms of emissions and fuel efficiency, at low power output as at high power output.
While these multi-engine “gen-set” locomotives are proving advantageous in many ways compared to traditional single engine locomotives, there are certain trade-offs. For example, the overall power density of the multi-engine “gen-set” locomotives is lower than an equivalent single engine locomotive. To date, the power density penalty has limited the application of the multi-engine idea to relatively low power locomotives like switchers or road switchers. Unless the power density can be improved, a high power multi-engine locomotive would likely be undesirably long.
In addition, at high power output, running three or four small engines in a multi-engine locomotive is not as efficient as running a single engine locomotive. So there is an efficiency penalty at high power outputs. A line haul locomotive typically runs at full power output more often than a switcher locomotive. For this additional reason, the multi-engine concept has been applied to date only to switcher locomotives.
This patent application describes a multi-engine locomotive configuration and operating method which minimizes these trade-offs, enabling an effective multi-engine configuration for a large locomotive like a line haul locomotive.